Püskürtme Beton Paneller İle Deprem Dayanımı Düşük Betonarme Çerçevelerin Güçlendirilmesi

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(1)İSTANBUL TECHNICAL UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY. RETROFITTING OF VULNERABLE REINFORCED CONCRETE FRAMES WITH SHOTCRETE WALLS. Ph.D. Thesis by Pınar TEYMÜR. Department :. Civil Engineering. Programme:. Structural Engineering. JUNE 2009.

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(3) İSTANBUL TECHNICAL UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY. RETROFITTING OF VULNERABLE REINFORCED CONCRETE FRAMES WITH SHOTCRETE WALLS. Ph.D. Thesis by Pınar TEYMÜR, M.Sc. (501992332). Date of submission: 10 March 2009 Date of defence examination: 8 June 2009. Co-Supervisor (Chairman): Prof. Dr. Sumru PALA Co-Supervisor : Assist. Prof. Dr. Ercan YÜKSEL Members of the Examining Committee Prof. Dr. H. Faruk KARADOĞAN (ITU) Prof. Dr. Feridun ÇILI (ITU) Prof. Dr. Tuncer ÇELİK (Beykent U.) Prof. Dr. Erdal İRTEM (Balıkesir U.) Assoc. Prof. Dr. Cem YALÇIN (BU). JUNE 2009.

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(5) İSTANBUL TEKNİK ÜNİVERSİTESİ FEN BİLİMLERİ ENSTİTÜSÜ. PÜSKÜRTME BETON PANELLER İLE DEPREM DAYANIMI DÜŞÜK BETONARME ÇERÇEVELERİN GÜÇLENDİRİLMESİ. DOKTORA TEZİ Pınar TEYMÜR (501992332). Tezin Enstitüye Verildiği Tarih : 10 Mart 2009 Tezin Savunulduğu Tarih : 08 Haziran 2009. Tez Danışmanı : Prof. Dr. Sumru PALA Yrd. Doç. Dr. Ercan YÜKSEL Diğer Jüri Üyeleri : Prof. Dr. H. Faruk KARADOĞAN (İTÜ) Prof. Dr. Feridun ÇILI (İTÜ) Prof. Dr. Tuncer ÇELİK (Beykent Ü.) Prof. Dr. Erdal İRTEM (Balıkesir Ü.) Doç. Dr. Cem YALÇIN (BÜ). HAZİRAN 2009.

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(7) FOREWORD I wish to express my gratitude to my co-supervisors Prof.Dr. Sumru Pala and Assist.Prof.Dr.Ercan Yuksel for their ideas, enthusiasm and encouragement. I am grateful for their guidance, support and assistance they have given me during my PhD. I would also like to thank Prof. Dr. Faruk Karadoğan and Prof. Dr. Feridun Çılı for his valuable inputs, suggestions and his support throughout the preparation of this thesis. I would like to thank the technicians at the Structural and Earthquake Engineering Laboratory for their invaluable technical assistance without them the experimental work would not have happened. I would like to express my thanks to Mahmut Şamlı and Hakan Saruhan, C.E., MSc for all the help with my experiments. I would like to thank Research Assist. Kıvanç Taşkın for his help during the tests. Special thanks must go to Dr. Cüneyt Vatansever who has helped me during the experiments and his friendship is appreciated. I would like to thank Assist.Prof. Dr. Rui Pinho especially for his contributions on the usage of SeismoStruct program and his guidance. I am indebted to him for providing me with the opportunity to conduct research in ROSE School, Italy. I would also like to thank the technicians of Structural Materials Laboratory and Assist.Prof.Dr. Hasan Yıldırım for all their help. I would like to thank Assoc.Prof.Dr. Hüseyin Yıldırım and Alternatif Zemin firm as without their help last two specimens could not be prepared. I would like to acknowledge the financial supports of TUBİTAK and ITU BAP division are appreciated. Finally I would like to thank my twin sister Assit.Prof.Dr. Berrak Teymur, my father Prof.Dr.Mevlut Teymur and my mother Duygu Teymur, Chemical Engineer, MSc, for their encouragement, faith, morale support and assistance during my difficult times.. March 2009. Pınar TEYMUR. v.

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(9) TABLE OF CONTENTS Page FOREWORD ..............................................................................................................v TABLE OF CONTENTS ........................................................................................vii ABBREVIATIONS ...................................................................................................ix LIST OF TABLES ....................................................................................................xi LIST OF FIGURES ................................................................................................xiii LIST OF SYMBOLS ..............................................................................................xix ÖZET .......................................................................................................................xxi SUMMARY ...........................................................................................................xxiii 1. INTRODUCTION ................................................................................................. 1 1.1. General ..............................................................................................................1 1.2. Objectives and Scope ........................................................................................2 1.3. Organization of the Thesis ................................................................................3 2. SEISMIC RETROFIT FOR REINFORCED CONCRETE BUILDING STRUCTURES ......................................................................................5 2.1. System Strengthening and Stiffening ...............................................................5 2.1.1 Shear walls .................................................................................................6 2.1.2 Carbon fiber reinforced polymer (CFRP) applied on the infill wall .........6 2.1.3 Braced frames ............................................................................................7 2.1.4 Moment resisting frames ...........................................................................8 2.1.5 Diaphragm strengthening ..........................................................................8 2.2. Enhancing Deformation Capacity ....................................................................8 2.2.1 Column strengthening ................................................................................9 2.2.2 Local stress reductions ............................................................................10 2.2.3 Supplemental support ..............................................................................10 2.3. Reducing Earthquake Demands .....................................................................10 2.3.1 Base isolation ...........................................................................................10 2.3.2 Energy dissipation systems ......................................................................11 2.3.3 Mass reduction .........................................................................................11 2.4. Rehabilitation Methods for Unreinforced Masonry Walls .............................11 2.4.1 Surface treatment .....................................................................................11 2.4.2 Injection grouting .....................................................................................13 2.4.3 Jacketing ..................................................................................................14 2.4.4 Reinforcing bars ......................................................................................14 2.4.5 Mechanical anchors .................................................................................15 2.5. What is Shotcrete ...........................................................................................16 2.5.1 Types of shotcrete according to the application process……..................17 2.5.2 Usage of shotcrete ...................................................................................18 2.5.3 Types of shotcrete ...................................................................................18 3. TEST PROGRAM AND MATERIAL CHARACTERIZATION …................21 3.1. Test Specimens ...............................................................................................21 3.2. Test Setup, Instrumentation and Data Acquisition .........................................31 .. .. .. .. .. .. .. .. .. .. .. .. vii.

(10) 3.2.1. Test setup and loading system ................................................................31 3.2.2. Instrumentation and data acquisition ......................................................32 3.3. Load Pattern ....................................................................................................35 3.4. Material Tests .................................................................................................36 3.4.1. Concrete tests ..........................................................................................37 3.4.2. Steel reinforcement tests .........................................................................38 .. 4. EXPERIMENTAL RESULTS ............................................................................39 4.1. Test Results of Specimen 1 ............................................................................39 4.2. Test Results of Specimen 2 …........................................................................42 4.3. Test Results of Specimen 2S ..........................................................................45 4.4. Test Results of Specimen 3 ............................................................................52 4.5. Test Results of Specimen 4 ............................................................................58 4.6. Test Results of Specimen 4S ..........................................................................60 4.7. Test Results of Specimen 5 ............................................................................68 4.8. Test Results of Specimen 6 ............................................................................74 4.9. Test Results of Specimen 7 ............................................................................81 4.10. Test Results of Specimen 8 ..........................................................................89 4.11. Evaluation of the Test Results ......................................................................95 4.11.1. Failure modes ........................................................................................95 4.11.2. Lateral load carrying capacity ..............................................................97 4.11.3. Initial stiffness .....................................................................................102 4.11.4. Cumulative energy dissipation ............................................................103 4.11.5. Equivalent damping characteristics ....................................................107 4.11.6. Lateral stiffness ...................................................................................109 4.11.7 Rotation of the panels...........................................................................112 5. ANALYTICAL STUDIES USING THE FINITE ELEMENT METHOD ...115 5.1. Nonlinear Static Analysis using SeismoStruct .............................................116 5.2. Description of Element Types Used .............................................................117 5.3. Material Models ............................................................................................117 5.3.1. Material model used for steel reinforcement ........................................118 5.3.2. Material model used for concrete .........................................................119 5.4. Inelastic Infill Panel Element ........................................................................121 5.5. Comparison of the Results of Analysis with Experimental Results .............130 5.5.1. Specimen 1 ............................................................................................133 5.5.2. Specimen 3 ............................................................................................136 5.5.3. Specimen 5 ............................................................................................140 5.5.4. Specimen 6 ............................................................................................145 5.5.5. Specimen 7 ............................................................................................149 6. PARAMETRIC STUDIES ................................................................................155 6.1. The Effect Panel Thickness ..........................................................................155 6.2. The Effect of the Distance between the Panel and the Frame ......................163 6.3. Panel Concrete Compressive Strengths ........................................................167 6.4. Application of the Retrofitting Technique to a Representative Frame .........170 7. CONCLUSIONS .................................................................................................189 REFERENCES .......................................................................................................193 VITA ........................................................................................................................201 . .. .. . .. .. . . .. .. .. .. viii.

(11) ABBREVIATIONS AC CFRP DC ED EDU FEMA FRP FRS LRB LVDT MTS RC SFRS STEEL SWAT TEC URM. : Alternative Current : Carbon Fiber Reinforced Polymer : Direct Current : Energy Dissipation : Energy Dissipation Units : Federal E M Agency : Fiber Reinforced Polymer : Fiber-Reinforced Shotcrete : Lead Rubber Bearings : Linear Variable Displacement Transducers : Material Test System : Reinforced Concrete : Steel Fiber-Reinforced Shotcrete : Structural and Earthquake Engineering Laboratory : Soil and Water Assessment Tool : Turkish Earthquake Code : Unreinforced Masonry Wall. ix.

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(13) LIST OF TABLES. Page No Table 3.1: Test specimens ...................................................................................23 Table 3.2: LVDTs used for bare frame ..............................................................33 Table 3.3: LVDTs used for fully infilled frame ..................................................33 Table 3.4: LVDTs used for partially infilled frame ............................................35 Table 3.5: Steps of the loading protocol .............................................................36 Table 3.6: Concrete mix proportions for frame concrete ....................................37 Table 3.7: Concrete mix proportions for shotcrete panel concrete .....................37 Table 3.8: The average concrete compressive strengths for frames ...................37 Table 3.9: The average concrete compressive strengths for panels ....................38 Table 3.10: Mechanical properties of steel bars .................................................38 Table 4.1: Width of cracks in mm at specific story drifts ...................................42 Table 4.2: Width of cracks in mm at specific story drifts ...................................45 Table 4.3: Width of cracks in mm at specific story drifts ...................................49 Table 4.4: Effect of strengthening in general ......................................................49 Table 4.5: Maximum base shears recorded during the tests ...............................50 Table 4.6: Initial stiffness of the specimens ........................................................50 Table 4.7: Width of cracks in mm at specific story drifts ...................................56 Table 4.8: Effect of strengthening in general ......................................................57 Table 4.9: Maximum base shears observed during the tests ...............................57 Table 4.10: Initial stiffness of the specimens ......................................................57 Table 4.11: Width of cracks in mm at specific story drifts .................................65 Table 4.12: Effect of strengthening in general ....................................................65 Table 4.13: Maximum base shears observed during the tests .............................66 Table 4.14: Initial stiffness of the specimens ......................................................66 Table 4.15: Width of cracks in mm at specific story drifts .................................71 Table 4.16: Effect of strengthening in general ....................................................72 Table 4.17: Maximum base shears occurred during the tests .............................72 Table 4.18: Initial stiffness of the specimens ......................................................72 Table 4.19: Width of cracks in mm at specific story drifts .................................78 Table 4.20: Effect of strengthening in general ....................................................79 Table 4.21: Maximum base shears observed during the tests .............................79 Table 4.22: Initial stiffness of the specimens ......................................................79 Table 4.23: Width of cracks in mm at specific story drifts .................................86 Table 4.24: Effect of strengthening in general ....................................................87 Table 4.25: Maximum base shears occurred during the tests .............................87 Table 4.26: Initial stiffness of the specimens ......................................................87 Table 4.27: Width of cracks in mm at specific story drifts .................................92 Table 4.28: Effect of strengthening in general ....................................................93 .. xi.

(14) Table 4.29: Maximum base shears observed during the tests .............................93 Table 4.30: Initial stiffness of the specimens ......................................................93 Table 4.31: Effect of retrofitting on general quantities .......................................96 Table 4.32: Maximum base shears observed during the tests .............................97 Table 4.33: Initial stiffness of the specimens ....................................................103 Table 5.1: Input parameters for steel reinforcement .........................................118 Table 5.2: Input parameters for concrete ..........................................................120 Table 5.3: Input parameters for the infill model ...............................................123 Table 5.4: Suggested and limit values for empiric parameters .........................126 Table 5.5: Input parameters of the shear spring ................................................127 Table 5.6: Limit strain values to define damage states in structural members according to TEC 2007 .....................................................132 Table 5.7: Damage levels for Specimen 1 .........................................................135 Table 5.8: Damage levels for Specimen 3 .........................................................139 Table 5.9: Damage levels for Specimen 5 .........................................................143 Table 5.10: Damage levels for Specimen 6 .......................................................147 Table 5.11: Damage levels for Specimen 7 .......................................................151 Table 6.1: The change in the thickness of the panel .........................................155 Table 6.2: The change in the distance between the column and the panel .......163 Table 6.3: The dimensions and reinforcement of the columns .........................172 Table 6.4: The reinforcement of the beams ......................................................172 Table 6.5: Concentrated mass values at each floor levels .................................173 Table 6.6: Forces applied during pushover analysis .........................................174 Table 6.7: Earthquake records ...........................................................................175 .. .. .. .. xii.

(15) LIST OF FIGURES. Page No Figure 2.1: Global modification of the structural system Thermou and Elnashai (2006) ..................................................................................5 Figure 2.2: Local modification of structural components, Thermou and Elnashai (2006) ...................................................................................9 Figure 3.1: General view of the fully infilled frame ...........................................21 Figure 3.2: General view of the partially infilled frame .....................................22 Figure 3.3: Geometry of the specimens ..............................................................25 Figure 3.4: Reinforcement details of the frame ..................................................26 Figure 3.5: Reinforcement details of the panel ...................................................26 Figure 3.6: Repairing process of the damaged bare frames ................................28 Figure 3.7: Construction of the shotcrete panels .................................................29 Figure 3.8: Specimen 6 and 7 having pre-reverse deflection on beam ...............30 Figure 3.9: Construction of Specimen 8 ….........................................................30 Figure 3.10: Test setup ........................................................................................31 Figure 3.11: Locations of LVDTs on bare frames ..............................................34 Figure 3.12: Locations of LVDTs on fully infilled frames .................................34 Figure 3.13: Locations of LVDTs on partially infilled frames ...........................34 Figure 3.14: Loading protocol ............................................................................36 Figure 4.1: Lateral load-top displacement curve of Specimen 1 ........................40 Figure 4.2: Envelope curve of Specimen 1 .........................................................40 Figure 4.3: Calculation of rotation at the ends of the columns ...........................41 Figure 4.4: Rotation at the bottom end of the right and left column ...................41 Figure 4.5: Rotation at the top end of the right and left column .........................41 Figure 4.6: Crack pattern of Specimen 1 at the end of test .................................42 Figure 4.7: Lateral load-top displacement curve of Specimen 2 .........................43 Figure 4.8: Envelope curve of Specimen 2 .........................................................43 Figure 4.9: Rotation at the bottom end of the right and left column ...................44 Figure 4.10: Rotation at the top end of the right and left column .......................44 Figure 4.11: Crack pattern of Specimen 2 at the end of test ...............................44 Figure 4.12: Lateral load-top displacement curve of Specimen 2S ....................45 Figure 4.13: Envelope curve of Specimen 2S .....................................................46 Figure 4.14: Rotation at the bottom end of the right and left column ................46 Figure 4.15: Rotation at the top end of the right and leftcolumn ........................46 Figure 4.16: Panel displacement .........................................................................47 Figure 4.17: Specimen 2S at the end of test .......................................................48 Figure 4.18: Crack pattern of Specimen 2S at the end of test ............................48 Figure 4.19: Comparison of envelope curves of Specimen 2S and Specimen 1 .....................................................................................49. xiii.

(16) Figure 4.20: The comparison of cumulative energy dissipation capacities of Specimens 1 and 2S ........................................................................50 Figure 4.21: Cumulative energy dissipation capacities of Specimens 1 and 2S at various story drifts .................................................................51 Figure 4.22: Lateral load-top displacement curves of Specimen 3 .....................52 Figure 4.23: Envelope curve of Specimen 3 .......................................................53 Figure 4.24: Rotation at the bottom end of the right and left column .................53 Figure 4.25: Rotation at the top end of the right and left column .......................53 Figure 4.26: Panel displacement .........................................................................54 Figure 4.27: Specimen 3 at the end of test ..........................................................55 Figure 4.28: Crack pattern of Specimen 3 at the end of test ...............................55 Figure 4.29: Comparison of envelope curves of Specimens 3 and 1 with analytical bare 3 .............................................................................56 Figure 4.30: The comparison of cumulative energy dissipation capacities of Specimens 1 and 3 ..........................................................................57 Figure 4.31: Cumulative energy dissipation capacities of Specimens 1 and 3 at various story drifts ......................................................................58 Figure 4.32: Lateral load-top displacement curve of Specimen 4 ......................59 Figure 4.33: Rotation at the bottom end of the right and left column .................59 Figure 4.34: Rotation at the top end of the right and left column .......................59 Figure 4.35: Crack pattern of Specimen 4 at the end of test ...............................60 Figure 4.36: Lateral load-top displacement curve of Specimen 4S ....................61 Figure 4.37: Envelope curve of Specimen 4S .....................................................61 Figure 4.38: Rotation at the bottom end of the right and left column .................62 Figure 4.39: Rotation at the top end of the right and left column .......................62 Figure 4.40: Panel horizontal displacement at top ..............................................62 Figure 4.41: Panel horizontal displacement at middle ........................................63 Figure 4.42: Panel horizontal displacement at bottom ........................................63 Figure 4.43: Specimen 4S at the end of test .......................................................64 Figure 4.44: Crack pattern of Specimen 4S at the end of test .............................64 Figure 4.45: Comparison of envelope curves of Specimens 4S and 1 with analytical bare 4S ...........................................................................65 Figure 4.46: The comparison of cumulative energy dissipation capacities of Specimens 1 and 4S .......................................................................66 Figure 4.47: Cumulative energy dissipation capacities of Specimens 1 and 4S at various story drifts ................................................................67 Figure 4.48: Lateral load-top displacement curve of Specimen 5 ......................68 Figure 4.49: The envelope curve of Specimen 5 .................................................69 Figure 4.50: Rotation at the bottom end of the right and left column .................69 Figure 4.51: Rotation at the top end of the right and left column .......................69 Figure 4.52: Specimen 5 at the end of test .........................................................70 Figure 4.53: Crack pattern of Specimen 5 at the end of test ..............................71 Figure 4.54: Comparison of envelope curves of Specimens 5 and 1 with analytical bare 5 .............................................................................72 Figure 4.55: The comparison of cumulative energy dissipation capacities of Specimens 1 and 4S .......................................................................73 Figure 4.56: Cumulative energy dissipation capacities of Specimens 1 and 5 at various story drifts .....................................................................73 Figure 4.57: Lateral load-top displacement curve of Specimen 6 ......................75 Figure 4.58: The envelope curve of Specimen 6 ................................................75 .. .. .. .. .. .. .. xiv.

(17) Figure 4.59: Rotation at the bottom end of the right and left column .................76 Figure 4.60: Rotation at the top end of the right and left column .......................76 Figure 4.61: Panel displacement .........................................................................76 Figure 4.62: Specimen 6 at the end of test ..........................................................77 Figure 4.63: Crack pattern of Specimen 6 at the end of test ...............................78 Figure 4.64: Comparison of envelope curves of Specimens 6 and 1 with analytical bare 6 .............................................................................79 Figure 4.65: The comparison of cumulative energy dissipation capacities of Specimens 1 and 6 ..........................................................................80 Figure 4.66: Cumulative energy dissipation capacities of Specimens 1 and 6 at various story drifts ...................................................................80 Figure 4.67: Lateral load-top displacement curve of Specimen 7 .......................82 Figure 4.68: The envelope curve of Specimen 7 .................................................82 Figure 4.69: Rotation at the bottom end of the right and left column .................83 Figure 4.70: Rotation at the top end of the right and left column .......................83 Figure 4.71: Panel horizontal displacement at top ..............................................83 Figure 4.72: Panel horizontal displacement at middle ........................................84 Figure 4.73: Panel horizontal displacement at bottom ........................................84 Figure 4.74: Specimen 7 at the end of test ..........................................................85 Figure 4.75: Crack pattern of Specimen 7 at the end of test ...............................85 Figure 4.76: Comparison of envelope curves of Specimens 7 and 1 with analytical bare 7 .............................................................................86 Figure 4.77: The comparison of cumulative energy dissipation capacities of Specimens 1 and 7 ..........................................................................87 Figure 4.78: Cumulative energy dissipation capacities of Specimens 1 and 7 at various story drifts ...................................................................88 Figure 4.79: Lateral load-top displacement curve of Specimen 8 ......................89 Figure 4.80: The envelope curve of Specimen 8 .................................................90 Figure 4.81: Rotation at the bottom end of the right and left column .................90 Figure 4.82: Rotation at the top end of the right and left column .......................90 Figure 4.83: Panel displacement .........................................................................91 Figure 4.84: Specimen 8 at the end of test ..........................................................92 Figure 4.85: Crack pattern of Specimen 8 at the end of test ...............................92 Figure 4.86: Comparison of envelope curves of Specimens 8 and 1 with analytical bare 8 .............................................................................93 Figure 4.87: The comparison of cumulative energy dissipation capacities of Specimens 1 and 8. .........................................................................94 Figure 4.88: Cumulative energy dissipation capacities of Specimens1 and 8 at various story drifts ......................................................................94 Figure 4.89: The comparison of envelope curves of Specimens 1, 2S and 3 ….98 Figure 4.90: The comparison of envelope curves of Specimens 2S and 3 with analytical 3_2S ...............................................................................98 Figure 4.91: The comparison of envelope curves of Specimens 1, 4S and 5 .....99 Figure 4.92: The comparison of envelope curves of Specimens 1, 3 and 6 ......100 Figure 4.93: The comparison of envelope curves of Specimens 3 and 6 with analytical 3_6 ...............................................................................100 Figure 4.94: The comparison of envelope curves of Specimens 1, 5 and 7 ......101 Figure 4.95: The comparison of envelope curves of Specimens 1, 6 and 7 ......101 Figure 4.96: The comparison of envelope curves of Specimens 1, 3, 5 and 8 ..102 Figure 4.97: The comparison of envelope curves of Specimens 1, 3, 5 and 8 .. xv.

(18) with analytical 3_8 and analytical 1_8 .……………....................102 Figure 4.98: Initial stiffnesses of the specimens ...............................................103 Figure 4.99: Cumulative energy dissipation capacities at various story drifts . 104 Figure 4.100: The comparison of cumulative energy dissipation capacities of Specimens 1, 2S and 3 ................................................................104 Figure 4.101: The comparison of cumulative energy dissipation capacities of Specimens 1, 4S and 5 ................................................................105 Figure 4.102: The comparison of cumulative energy dissipation capacities of Specimens 1, 3 and 6 ..................................................................105 Figure 4.103: The comparison of cumulative energy dissipation capacities of Specimens 1, 5 and 7 ..................................................................106 Figure 4.104: The comparison of cumulative energy dissipation capacities of Specimens 1, 6 and 7 ..................................................................106 Figure 4.105: The comparison of cumulative energy dissipation capacities of Specimens 1, 3, 5 and 8 ..............................................................107 Figure 4.106: Dissipated and strain energy .…………………….…………….108 Figure 4.107: Equivalent damping for various tests ………………………….108 Figure 4.108: The comparison of lateral stiffnesses of Specimen 1, 2S and 3 .109 Figure 4.109: The comparison of lateral stiffnesses of Specimen 1, 4S and 5 .109 Figure 4.110: The comparison of lateral stiffnesses of Specimen 1, 3 and 6 ...110 Figure 4.111: The comparison of lateral stiffnesses of Specimen 1, 5 and 7 ...110 Figure 4.112: The comparison of lateral stiffnesses of Specimen 1, 6 and 7 ...111 Figure 4.113: The comparison of lateral stiffnesses of Specimen 1, 3, 5 and 8111 Figure 4.114: Calculation of rotation of the shotcrete panel .…………………112 Figure 4.115: The rotation of the panel for Specimen 3 ……………………...113 Figure 4.116: The rotation of the panel for Specimen 5 ……………………...113 Figure 4.117: The rotation of the panel for Specimen 8 ……………………...114 Figure 5.1: Fibre analysis approach ..................................................................116 Figure 5.2: Gauss Integration points in beam column elements ………….......117 Figure 5.3: Strut model used .............................................................................122 Figure 5.4: General characteristics of the proposed model for cyclic axial behaviour of masonry, Crisafulli, 1997 .………………………….122 Figure 5.5: Analytical response for cyclic shear response of mortar joints ..…127 Figure 5.6: Change in the strut area …………………………………………..129 Figure 5.7: Frame model used in SeismoStruct ………………………………131 Figure 5.8: Infilled frame models used in SeismoStruct .……………………..131 Figure 5.9: Definition of frame element names and the loadings in the mathematical model used in SeismoStruct .………………………132 Figure 5.10: The displacement pattern applied to Specimen 1 ……………….133 Figure 5.11: Comparison of the hysteretic curves of the experimental and analytical results of Specimen 1 .………………………………..133 Figure 5.12: Comparison of the envelope curves of the experimental and analytical results of Specimen 1 .………………………………..134 Figure 5.13: Damage states obtained at drift levels at certain drift levels at Specimen 1 ……………………………………………………...136 Figure 5.14: Damages occurred at the end of the analysis at Specimen 1 ……136 Figure 5.15: The displacement pattern applied to Specimen 3 ……………….137 Figure 5.16: Comparison of the hysteretic curves of the experimental and analytical results of Specimen 3 .………………………………..137 Figure 5.17: Comparison of the envelope curves of the experimental and. xvi.

(19) analytical results of Specimen 3 .…………………………….….138 Figure 5.18: Damage states obtained at drift levels at certain drift levels at Specimen 3 …………………………………………………..….140 Figure 5.19: Damage occurred at the end of the analysis at Specimen 3 .….....140 Figure 5.20: The displacement pattern applied to Specimen 5 …………….....141 Figure 5.21: Comparison of the hysteretic curves of the experimental and analytical results of Specimen 5 .………………………………..141 Figure 5.22: Comparison of the envelope curves of the experimental and analytical results of Specimen 5 .………………………………..142 Figure 5.23: Damage states obtained at drift levels at certain drift levels at Specimen 5 ……………………………………………………...144 Figure 5.24: Damage occurred at the end of the analysis at Specimen 5 .…….145 Figure 5.25: The displacement pattern applied to Specimen 6 ……………….145 Figure 5.26: Comparison of the hysteretic curves of the experimental and analytical results of Specimen 6 .………………………………..146 Figure 5.27: Comparison of the envelope curves of the experimental and analytical results of Specimen 6 .………………………………..146 Figure 5.28: Damage states obtained at drift levels at certain drift levels at Specimen 6 ……………………………………………………...148 Figure 5.29: Damage occurred at the end of the analysis at Specimen 6 .….....149 Figure 5.30: The displacement pattern applied to Specimen 7 ……………….149 Figure 5.31: Comparison of the hysteretic curves of the experimental and analytical results of Specimen 7 .………………………………..150 Figure 5.32: Comparison of the envelope curves of the experimental and analytical results of Specimen 7 .………………………………..150 Figure 5.33: Damage states obtained at drift levels at certain drift levels at Specimen 7 ……………………………………………………...152 Figure 5.34: Damage occurred at the end of the analysis at Specimen 7 .…….153 Figure 6.1: Lateral load-top displacement curves for the infill panel thickness changes in Specimen 3 ………………………………...156 Figure 6.2: Envelope curves for the thickness changes in Specimen 3 ………156 Figure 6.3: Initial stiffness of Specimen 3 for the change in panel thickness ...157 Figure 6.4: The comparison of cumulative energy dissipation capacities of Specimen 3 for the change in panel thickness .…………...………158 Figure 6.5: Base shear-top displacement curves for the infill panel thickness changes in Specimen 3 ………………………………...159 Figure 6.6: Envelope curves for the thickness changes in Specimen 3 ………159 Figure 6.7: Lateral load-top displacement curves for the infill panel thickness changes in Specimen 5 ……………………………..….160 Figure 6.8: Envelope curves for the thickness changes in Specimen 5 ………160 Figure 6.9: Initial stiffness of Specimen 5 for the change in panel thickness ...161 Figure 6.10: The comparison of cumulative energy dissipation capacities of Specimen 5 for the change in panel thickness ..…………………162 Figure 6.11: The gap, a, and the distance between the inside face of the columns, L, in the model used .…….……………………………163 Figure 6.12: Lateral load-top displacement curves for the gap size changes in Specimen 5 …………………………………………………...164 Figure 6.13: Envelope curves for the gap size changes in Specimen 5 ..….…..165 Figure 6.14: The comparison of cumulative energy dissipation capacities of Specimen 5 for the gap size changes .……………………….......166 .. xvii.

(20) Figure 6.15: Base shear-top displacement curves for the infill panel concrete compressive changes in Specimen 3 .……………….…168 Figure 6.16: Envelope curves for the infill panel concrete compressive changes in Specimen 3 ……………………………………..…...168 Figure 6.17: Initial stiffness of Specimen 3 for the infill panel concrete compressive changes ………………………………………..…..169 Figure 6.18: The comparison of cumulative energy dissipation capacities of Specimen 3 for the infill panel concrete compressive changes ....170 Figure 6.19: The representative frame ……………………………………..…171 Figure 6.20: Retrofitting of the frame by shotcreted walls …………………...171 Figure 6.21: Cross section of the column .………………………………….....172 Figure 6.22: Cross section of the typical beam ……………………………….172 Figure 6.23: Constitutive models used in analytical study .…………………...173 Figure 6.24: First mode shapes of bare and retrofitted frame ………………...174 Figure 6.25: Base shear-top displacement and base shear/total weight-top displacement/total height diagram ……………………………...175 Figure 6.26: The acceleration record of Erzincan Earthquake .……………….176 Figure 6.27: The acceleration record of İzmit Earthquake .…………………...176 Figure 6.28: The acceleration record of Düzce Earthquake .………………….176 Figure 6.29: “Service” type acceleration records .…………….……………....177 Figure 6.30: “Design” type acceleration records …………….……………….177 Figure 6.31: Design spectrum defined in TEC, 2007 .………………………...173 Figure 6.32: Time versus top displacement graphs for bare and retrofitted frame under service earthquakes ……………………………..…179 Figure 6.33: Time versus base shear force graphs for bare and retrofitted frame under service earthquakes ………………………………..180 Figure 6.34: Time versus top displacement graphs for bare and retrofitted frame under design earthquakes .………………………………..181 Figure 6.35: Time versus base shear force graphs for bare and retrofitted frame under design earthquakes .……………………………..…182 Figure 6.36: Comparison of the maximum story displacements of the frame with and without shotcrete panel for service and design earthquakes .…………………………………………………..…183 Figure 6.37: Comparison of the maximum interstorey drift of the frame with and without shotcrete panel for service and design earthquakes .…………………………………………………..…183 Figure 6.38: Comparison of the maximum interstorey shear force of the frame with and without shotcrete panel for service and design earthquakes .…………………………………………………..…184 Figure 6.39: Performance of the bare and retrofitted systems under design earthquakes .……………………………………………………..185 Figure 6.40: Comprasion of the reinforcement strains of some critical sections with and without shotcrete panel for design Düzce earthquake .……………………………………………………...186 Figure 6.41: Comprasion of the reinforcement strains of some critical sections with and without shotcrete panel for design Erzincan earthquake ………………………………………………………187 .. .. xviii.

(21) LIST OF SYMBOLS a1 a2 A1 A2 bw D dm Dr Dur EcIc Em Es Esp ex1 ex2 fc fmax fmθ Fr ft ft Fu fult fy H hw hz KA KS kc L li(t) P Pi Pi0 Pmax Pultimate r R0 t x Xoi. : Transition Curve Shape Calibrating Coefficients : Transition Curve Shape Calibrating Coefficients : Strut Area 1 : Strut Area 2 : Equivalent width of the strut : Longitudinal Bar Diameter : Diagonal of the infill panel : Lateral Displacement for Retrofitted Specimen : Lateral Displacement for Unretrofitted Specimen : Bending stiffness of the columns : Initial Young modulus of wall : Modulus of Elasticity of Reinforcement : Post-yield Stiffness : Plastic unloading stiffness factor : Repeated cycle strain factor : Compressive Strength of Concrete : Maximum Stress of Reinforcement : Compressive strength of wall : Lateral Resistance for Retrofitted Specimen : Tensile Strength of Concrete : Tensile strength of wall : Lateral Resistance for Unretrofitted Specimen : Ultimate Stress Capacity : Yield Stress of Reinforcement : Specimen Height : Height of the infill panel : Equivalent contact length : Strut stiffness : Shear stiffness : Confinement factor : Transverse Reinforcement Spacing : Load Factor : Kinematic/isotropic Weighing Coefficient : The applied load in a nodal position i : Nominal Load : Maximum Load : Ultimate Load : Spurious Unloading Corrective Parameter : Transition Curve Initial Shape Parameter : Infill Panel Thickness : Column Width : Horizontal offsets xix.

(22) Yoi Z αch αre. αs. βa βch. δ ∆max ∆ultimate ε1 ε2 εc εcl εm εsu εult γ γplr γplu γun. γs Λ µ µ τmax τ0 θ. : Vertical offsets : Actual contact length : Strain inflection factor : Strain reloading factor : Reduction shear factor : Complete unloading strain factor : Stress inflection factor : Displacement : Maximum Displacement : Ultimate Displacement : Strut area reduction strain of wall : Residual strut area strain of wall : Strain at peak stress : Closing strain of wall : Strain at maximum stress of wall : Ultimate Strain of Reinforcement : Ultimate Strain Capacity : Specific weight : Reloading stiffness factor : Zero stress stiffness factor : Starting unloading stiffness factor : Proportion of stiffness assigned to shear : Dimensionless relative stiffness parameter : Friction coefficient : Strain Hardening Parameter : Maximum shear strength : Shear bond strength : Angle of the diagonal strut with respect to the beams. xx.

(23) DEPREM. GÜVENLİĞİ. YETERSİZ. BETONARME. ÇERÇEVELERİN. PÜSKÜRTME BETON PANELLER İLE GÜÇLENDİRİLMESİ. ÖZET Deprem güvenliği yetersiz olan yığma ve betonarme binaların güçlendirilmesinde kullanılmakta olan yöntemlerden biri, sistemde var olan dolgu duvarlara püskürtme beton uygulamasıdır. Bu uygulamadan yola çıkarak, püskürtme beton ve hasır donatı ile oluşturulan panellerin, betonarme çerçevelerin güçlendirilmesinde kullanılması konusu bu tez çalışmasında ele alınmıştır. Çalışma, deneysel ve analitik olmak üzere iki bölümden meydana gelmektedir. Püskürtme beton ile oluşturulan panelin çerçeve davranışına katkısı, deneysel çalışma ile araştırılmıştır. Ülkemizdeki binaların çoğunluğunu temsil edebilmek amacıyla, deprem güvenliği yetersiz, güçlü kiriş/zayıf kolonlardan oluşan bir betonarme çerçeve ele alınmış ve bu çerçeve yaklaşık ½ geometrik ölçekle küçültülerek deney numunesinin boyutları ve kesit özellikleri belirlenmiştir. Bu betonarme çerçeveler, içerisine klasik tuğla duvar yerine hasır donatı ve ıslak karışımlı püskürtme beton ile oluşturulmuş paneller yerleştirilerek güçlendirilmiştir. Toplam sekiz adet numune üretilmiştir. Numunelerden biri panelsiz bırakılan yalın çerçeve, bir diğeri ise içerisine geleneksel betonarme perde yerleştirilen perdeli çerçevedir. Bu şekilde üretilen yalın çerçeve ve perdeli çerçeve referans çerçevesi olarak kullanılmıştır. Numunelerden dört tanesi hasarsız betonarme çerçevenin, püskürtme beton ve hasır donatı ile oluşturulan paneller ile güçlendirilmesi ile elde edilen standart deney numuneleridir. Son iki numune ise, önceden hasar verilmiş ve tamir edilmiş betonarme çerçevenin püskürtme beton ve hasır donatı ile oluşturulan paneller ile güçlendirilmesi ile elde edilen deney numuneleridir. Numuneler, panelin çerçeveye bağlantısı bakımından iki gruba ayrılmaktadır. Birinci grup numunelerde, panel tüm çevresi boyunca çerçeveye bağlanmıştır. İkinci grup numunelerde ise panel sadece alt ve üstten kirişlere bağlanmış, kolonlara mesafeli olarak yerleştirilmiştir. Tek katlı, tek açıklıklı olarak üretilen numuneler, kolonlar üzerine etkiyen sabit eksenel yükler ile kiriş hizasından etkiyen tersinir tekrarlı yatay yükler etkisinde denenmiştir. Çalışmanın kuramsal bölümünde; yapı sistemlerinin doğrusal olmayan analizini yapan SeismoStruct programı kullanılarak, deneysel olarak incelenen numunelerin kuramsal modelleri oluşturulmuştur. Bu kuramsal modellerde elde edilen kesit ve sistem davranışlarına ait büyüklükler, deneysel sonuçlar ile karşılaştırılmış ve yorumlanmıştır. Deneysel ve kuramsal çalışmalar sonucunda; önerilen güçlendirme yönteminin betonarme çerçevenin yatay yük taşıma kapasitesi, yatay rijitlik ve enerji sönümleme özelliklerini önemli ölçüde arttırdığı görülmüştür. Önerilen yöntemin, binaların xxi.

(24) depreme karşı güçlendirmesinde hızlı, kolay ve ucuz bir teknik olarak kullanılabileceği düşünülmektedir.. xxii.

(25) RETROFITTING OF VULNERABLE REINFORCED CONCRETE FRAMES WITH SHOTCRETE PANELS. SUMMARY Application of shotcrete concrete on the walls within the existing vulnerable reinforced concrete and masonry buildings is a known retrofitting technique. As an alternative to this application, construction of shotcrete infill panels in bare reinforced concrete frames is aimed in this thesis. The suggested method can be beneficial against conventional shear wall, when formwork and workmanship is expensive and accessing to the work area is difficult. The study consists of experimental and analytical parts. In the experimental part, to evaluate the effectiveness of this retrofitting technique, an experimental research program was accomplished. Infill panels made from wetmixed shotcrete in lieu of a traditional masonry are used in vulnerable reinforced concrete frames. The frames were chosen to represent weak column/strong beam type structures that were very common in Turkey especially for the buildings constructed before the two latest earthquake codes. The experimental work is composed of strengthening of four undamaged and two damaged frames with shotcrete panels and a bare frame and a conventional shear wall specimens as a reference. Nearly ½ scale, one bay- one story specimens were tested under constant vertical loads acting on the columns and lateral reversed cycling loads. The infill panels are connected to the surrounding reinforced concrete frame in two different ways. In the first case, full integration along four edges of the infill panel is achieved. In the second case, the infill panel is connected only to the beams of the frame having a distance between the columns and edges of the infill panel. To evaluate effectiveness of the proposed technique, response parameters of the retrofitted frame experiments were compared with those of the bare frame’s and the conventional shear wall’s. In the analytical part of the thesis, SeismoStruct, a nonlinear finite element computer analysis program, has been used to generate the theoretical models of the tested specimens. The sectional and overall behaviors of the frames obtained from experimental and analytical works are compared with each other. The experimental and analytical studies show that the proposed retrofitting technique for vulnerable reinforced concrete frames increases the lateral load carrying capacity, the lateral rigidity and the energy dissipation capacity of the system. It is considered that the suggested technique can be used as an efficient, easy and cost effective method in retrofitting the existing vulnerable reinforced concrete buildings.. xxiii.

(26) xxiv.

(27) 1. INTRODUCTION 1.1 General The existence of many vulnerable reinforced concrete buildings in earthquake prone areas built before the current Turkish earthquake code, presents one of the most serious problems facing Turkey, especially in Istanbul today. During 1999 Kocaeli Earthquake, buildings had greater damage than expected at that magnitude of an earthquake in the city. Since then researchers have been trying to find out cheap and easily applicable strengthening solutions for the vulnerable reinforced concrete (RC) and masonry buildings. The experiments carried on, show that infill walls increase the lateral load carrying capacity and the lateral stiffness of the structures, (Klingner and Bertero, 1978, Govindan et al. 1986, Al-Chaar et al. 1996, Lee and Woo 2002). It can be stated that when the necessary precautions are taken, the infill walls can be used to strengthen the building against lateral loads, (Sugano and Fujimura, 1980, Zarnic and Tomazevic, 1984, Altin et al. 1992). Strengthening a damaged RC frame with forming a thin concrete wall on the existing masonry walls (Zarnic and Tomazevic 1988, Yuksel et al. 1998a and 1998b) or using shotcrete on special wall-like structures in lieu of masonry walls (Mourtaja et al. 1998) showed that, these kinds of easily applicable retrofitting techniques increases lateral load carrying capacity and lateral rigidity of the structure. Strengthening of infill walls using shotcrete is typically used in strengthening of damaged and/or undamaged masonry buildings in Turkey as stated in the studies of Wasti et al. (1997), Celep (1998), Aydoğan and Öztürk (2002). In this thesis, using shotcrete panels in lieu of traditional masonry walls in reinforced concrete buildings is proposed and the overall responses of these frames responding in-plane lateral loading are investigated.. 1.

(28) 1.2 Objectives and Scope In this study wet-mixed sprayed concrete is used to form an infill wall within a vulnerable RC frame. Nearly ½ scale, one story, one bay specimens were tested under constant vertical loads acting on the columns and lateral reversed cycling loads. The experimental work is composed of testing one bare frame for reference, six vulnerable RC frames by forming an infill wall using wet-mixed sprayed concrete and one conventional shear wall. In four of them, the walls are connected to the frames through shear studs used at four edges of them to create strong bond between walls and the members of the frames. In three of them; the walls are connected only to the beams through shear studs used at two edges of the infill wall, while the other two edges are distanced to the columns. One of the specimens from each group is slightly damaged and repairing of cracks has taken place before strengthening with shotcrete panels. Pre-reverse deflection is applied to the beam during construction of the shotcrete panel for the other two. The main objectives of this research are: 1) To find out fast, cheap and adequate retrofitting techniques for vulnerable RC structures, 2) To set up and conduct a test program to investigate the behaviour of RC frames infilled with wet-mixed shotcrete panels, and to characterize the strength and stiffness behaviour of these frames responding to in-plane lateral loading. In order to fulfill the objectives stated above, the following summarizes the work done in this study as undertaken in chronological order: 1) State the need for retrofitting the vulnerable RC frames and the advantages of using wet-mixed shotcrete (this will be stated in the upcoming literature review) 2) Select a reasonable testing scale considering the capacities of the testing facilities in Structural and Earthquake Engineering Laboratory of Istanbul Technical University (STEEL). 3) Conduct the standard material tests for the four different materials used, namely: frame concrete, shotcrete concrete, frame steel and panel steel.. 2.

(29) 4) Perform the main experimental program to investigate the effect of the shotcrete panel addition to the system. 5) A finite element program, named as SeismoStruct is used to develop an analytical model which is used for modelling the response of RC frames retrofitted with shotcrete panels. The experimental results were verified using the analytical models in the program. 6) Investigate the effects of the proposed retrofitting technique on a representative frame by using the analytical model developed for the response of the shotcrete wall, 1.3 Organization of the Thesis This thesis is composed of seven chapters. Following this chapter, Chapter 2 explores the other retrofitting techniques as well as the types of shotcrete and tries to state the advantages of using wet-mixed shotcrete that is used in this study. The experimental program is given in Chapter 3. The geometry and reinforcement details of the specimens, the data acquisition and loading system, and the results of material tests are also presented. The experimental results which discuss the effect of retrofitting the RC frames with wet-mixed shotcrete panels are given briefly in Chapter 4. The analytical model used is explained in Chapter 5 and also the proposed model is verified using the experimental results. By using the analytical models developed, a parametric study is performed in Chapter 6. The panel thickness, the concrete compressive strength of the panel, the distance between the frame and the panel are the parameters that are examined in this study. The effect of the proposed retrofitting technique on a 2D frame of building representing the typical reinforced concrete frame type structures in Turkey is also discussed in this chapter. Finally, conclusions are presented in Chapter 7.. 3.

(30) 4.

(31) 2. SEISMIC RETROFIT FOR REINFORCED CONCRETE BUILDING STRUCTURES The ways to enhance the seismic capacity of existing structures are usually considered in two main ideas. First one is based on increasing the strength and stiffness of the structural system which can be done by major modifications to it. These modifications include the addition of structural walls, steel braces. The second way is based on deformation capacity of the components of the system. Here the ductility of components with inadequate capacities is increased and their specific limit states are satisfied. Retrofitting of each component of the system involves methods like the addition of concrete, steel or fiber reinforced polymer (FRP) jackets to columns for confinement. 2.1 System Strengthening and Stiffening Strengthening the system increases the total lateral force capacity of the system. When the seismic capacity of the existing structures is improved, the performance of the building is moved to a better level by the stiffening of the system. The retrofitting methods of existing structures are described below briefly. The influences of these methods on the overall behaviour of the structure are summarized in Figure 2.1.. Figure 2.1: Global modification of the structural system, Thermou and Elnashai (2006). 5.

(32) The methods listed below are some of the repair and strengthening methods used for existing concrete structures. 2.1.1 Shear walls Placing of reinforced concrete shear walls into an existing building is one of the most common methods used as repair and strengthening of structures. Although it increases the strength and stiffness of vulnerable buildings it is necessary to evacuate the habitants of the building during the construction. Shear walls are efficient in controlling the overall lateral drifts and thereby reducing damage in frame members. Application of shear walls involves partial or total infilling of some of the bays of the frame. Existing infill walls can also be turned into shear walls and shotcrete can be used instead of regular concrete to increase the adherence between the existing and new material. To reduce time and cost, precast panels can be used as well. Many research on structural walls and results of detailed applications have been reported, (Sugano and Fujimura 1980, Yuzugullu 1980, Higashi et al. 1980, Altin et al. 1992, Pincheira and Jirsa 1995, Frosh et al. 1996, Lombard et al. 2000, Inukai and Kaminosono 2000). The results show that the response of panels with the structure depends mainly on the application details. Proper anchorage of re-bars to beams and closely spaced mesh increases the deformation abilities and the strength is increased by full continuity between levels. If there is poor detailing and lack of load transfer between old and new members, this may lead to brittle failure of infill panels or reduction of ductility of the system. One down side of the method is the need to strengthen the foundations. The strengthening is necessary, so that the foundations can resist the increased weight of the structure and the overturning moment. The application of this technique is usually costly, disruptive and unsuitable for building with an insufficient foundation system. 2.1.2 Carbon fiber reinforced polymer (CFRP) applied on the infill wall Another method used in the rehabilitation of reinforced concrete structures is strengthening infill walls with fiber reinforced polymers (FRP). This technique improves the seismic performance of structures in terms of strength, stiffness and energy. 6.

(33) dissipation capacity. When it is compared with other techniques, it is very simple and fast to apply and it is an efficient method because evacuation of the building is not required during the process, however it is expensive. Marshall and Sweeney (2004) tested the effect of FRP strengthening. They observed that the failure mode of wall sections has also been changed by the different FRP configurations. As can be seen by these tests, FRP composites can be applied to increase the strength and change the failure mode of masonry walls in shear. Erol et al. (2004, 2005, 2006 and 2008) performed a series of tests for examining the differences between the structural behaviour of infilled RC frames strengthened by CFRP fabric with different connection details. They observed that, the existence of CFRP keeps the brittle wall to fall apart and hence contributes to the overall in-plane and out- of-plane stability of structure during the load reversals. 2.1.3 Braced frames Bracing frames with steel is one of the other methods to strengthen. However it does not provide as much strength and stiffness as the shear walls method. Mass of braced frames is less than the shear walls’ and they do not increase the building mass significantly. Therefore seismic forces induced by the lateral load do not increase. Steel bracings are usually installed between existing members and an improvement for the foundation system might not be necessary. It is difficult to connect bracing steel members to the existing concrete structure and the connections are vulnerable during earthquakes. The addition of steel bracing is effective for the strengthening and stiffening of existing buildings. In the selected bays of an RC frame, to increase the lateral resistance of the structure, concentric or eccentric bracings can be used. Successful results of usage of steel bracing to upgrade RC structures have been reported by several researches; (Sugano and Fujimura 1980, Higashi et al. 1984, Badoux and Jirsa 1990, Miranda and Bertero 1990, Bush et al. 1991, Teran-Gilmore et al. 1995, Pincheira and Jirsa 1995, Goel and Masri 1996). After the 1985 Michoacan Earthquake a series of RC buildings retrofitted with steel bracing have been reported with no structural damage (Del Valle 1980, Foutch et al. 1988). 7.

(34) Taşkın et al. (2007) have examined effects of different types of bracings with different geometrical characteristics on the behavior of the system. In this study, instead of using conventional bracing system, a new concept has been tested and compared with the other systems. This approach is called as "Disposable Knee Bracing" and parametric analytical studies done giving successful results. As expected bracing has increased the horizontal load carrying capacity and energy absorption capacity, and most importantly, reduced the amount of damage on the main structure. After obtaining these promising results Yorgun et al. (2008) have done the experiments of these analytical models and come up with close results. To increase damping; shear links and passive energy dissipation devices may also be used with bracings (Okada et al., 1992, Martinez-Romero, 1993). The addition of posttensioned rods, which will yield at smaller deformations to the system, will allow energy dissipation at early stage of a large event. The initial brace prestressing induces additional forces in the structure and the internal force distribution is modified. These need to be considered for serviceability limit states. 2.1.4 Moment resisting frames Moment resisting frames placed in buildings improve strength of the structure. Its advantage is that they occupy minimum floor space. However they have large lateral drift capacity when compared to the building they are placed in and this limits their use and cause the main problem for the system. 2.1.5 Diaphragm strengthening Diaphragm strengthening uses methods such as topping slabs, metal plates laminated onto the top of the slab surface, bracing diaphragms below the concrete slabs and increasing the existing nailing in the covering. The covering can be replaced with stronger material or for buildings with timber diaphragms they could be replaced with plywood. 2.2 Enhancing Deformation Capacity To enhance deformation capacity; column jacketing, strengthening and providing additional supports at places subjected to deformation are used. Below these will be explained in detail.. 8.

(35) The methods to increase the deformation capacity of existing structures are described below briefly. How these methods affect the behaviour of the structure is summarized in Figure 2.2.. Figure 2.2: Local modification of structural components, Thermou and Elnashai (2006). 2.2.1 Column strengthening For building with strong beam-weak column configurations, column strengthening is necessary as it will permit larger drifts and story mechanisms to be formed. In the seismic performance of a structure, column retrofitting is often critical as columns should not be the weakest components in the building structure. To increase the shear and flexural strength of columns, column jacketing may be used so that columns will not be damaged. The welding of the links between the new and existing reinforcement bars only need specialist knowledge. Rodriguez and Park (1991), Al-Chaar et al. (1996), Bousias et al. (2005), observed good results in their research. Confining of columns with continuous steel plates and with fiber reinforced plastic fibers are the two techniques that jacketing can be made. Recent research has also shown the applications of composites especially fiber reinforced polymer (FRP) materials used as jackets when retrofitting columns. As these jackets confine the columns, column failure due to forming of a plastic hinge zone is prevented. The uncertainty of the bond between the jacket and the original member is the main disadvantage of this method. Jacketing up of the slab has to be done before the construction of the jacketing of the column. If it is not done, then the load sharing does not take place until some large. 9.

(36) seismic displacement has occurred. Until then this can cause considerable cracking, even under small frequent earthquakes. 2.2.2 Local stress reductions Local stress reductions are applied to the elements which do not effect the performance of the building primarily. These can be done by demolition of local members that are not stiff and introducing joints between face of the column and adjacent architectural elements. 2.2.3 Supplemental support Supplemental bearing supports are used on the gravity load bearing structural elements which are not effective in resisting lateral force induced by an earthquake. 2.3 Reducing Earthquake Demands Reducing earthquake demands involve new and expensive special protective systems which modify the demand spectrum of the building while other methods improve the capacity of the building. The special protective systems are appropriate to use for important buildings such as historical buildings or for buildings which accommodate valuable equipments and machinery. Base isolation, energy dissipation systems and mass reduction are the methods used in reducing earthquake demands will be explained briefly below. 2.3.1 Base isolation In the upgrading of historical monuments, seismic isolation is accepted because it causes minimal disturbances. It is also applied in the upgrading of RC structures which are critical and need to be operational after seismic events. The aim of base isolation is to isolate the structure from the ground motion during earthquakes. This is achieved by installing bearings between the superstructure and its foundation. As most bearings have good energy dissipation characteristics, this method is effective for relatively stiff buildings with low rises and heavy loads. Kawamura et al. (2000), applied seismic isolation technique to two middle-rise reinforced concrete buildings in Japan. One is a 16 story building, which was upgraded by lead rubber bearings (LRB's) were installed in their mid-height in 22 columns on the 8th story. Due to the reduction of seismic force by isolation, strengthening of the 10.

(37) structure is not necessary. The other building has 7 stories and is supported on piles, where base isolation method was adopted. After cutting off the head of piles, rubber and sliding isolators were installed in parallel. Therefore strengthening of the super structure has come to be unnecessary. Base or seismic isolation methods are efficient in reducing response acceleration and interstorey drift which minimize structural and nonstructural damage. 2.3.2 Energy dissipation systems Another method is using energy dissipation units (EDUs). These systems are used to reduce the displacement demands on the structure by the energy dissipation and are most effective when used in structures with great lateral deformation capacity. Frame structures are appropriate for these systems. These systems can also be used to protect critical systems and contents in a building. Energy dissipation equipments are added to a structure via installing frictional, hysteretic or visco-elastic dampers as parts of braced frames. Many researchers have studied these energy dissipation methods, (Gates et al. 1990, Pekcan et al. 1995, Fu 1996, Tena-Colunga et al. 1997, Munshi 1998, Kunisue et al. 2000 and Kawamura et al. 2000). However, these methods are expensive and the application of them to all structures is costly. 2.3.3 Mass reduction Mass reduction which decreases the natural period of the building is one of the methods used to lessen the demand on buildings. It can be done by removing some of the stories in the building. 2.4 Rehabilitation Methods for Unreinforced Masonry Walls Various rehabilitation methods for unreinforced masonry walls (URM) exist and they can be listed as surface treatment, injection grouting, jacketing, internal reinforcement and mechanical fasteners. They will be explained in detail below. 2.4.1 Surface treatment Surface treatment can be done by various materials and procedures. The most common types of surface treatment involve using reinforced plaster, shotcrete and ferrocement which are applied on top of a metal grid that is anchored to the existing wall. Hutchinson 11.